Combine columns passed as parameters in QGIS graphical modeller

Question

I would like to combine two fields in QGIS using graphical modeller. If I were to do it using field calculator, I would do it as follows:

"field1" + ", " + "field2"

Unfortunately, I cannot do it, as I want those fields to be passed as parameters in the graphical modeller.

I have the following model:

As you can see, I have two parameters: "Calle" and "Portal", which are fields of the input vector layer. I would like to combine both fields using the field calculator algorithm. I need to pass the fields' names as parameters as I am looking for a generic solution that may work for different field names.

I have tried with the following formula in the field calculator algorigthm:

Unfortunately, instead of combining the parameters' values, it combines the parameters' names. Therefore, I tried with the parameter() function, which I assume should pass not the parameter itself but its value, as follows:

Unfortunately, when doing so, I get an empty result.

Is there any way to achieve what I am looking for?

Answer 1

You need to use the eval() function in your expression to get the actual value of the vector field variable instead of the variable name, like this:

eval(@field1) + ', ' + eval(@field2)

More details in the docs: https://docs.qgis.org/testing/en/docs/user_manual/working_with_vector/expression.html#general-functions

Answer 2

You can use the + operator when you want to make a sum of two numeric fields.

When you have at least one field that is not numeric, the addition is not possible and to combine the two, you have to use the concatenation operator ||.

Try the following command: field1 || ',' || field2